Are you saying that the currency switcher ALONE is slowing your site by 7 seconds? I seriously doubt it.
I use it on 8 sites and they all load between 1-4 seconds. There are other factors involved.
Look into those other factors (Image size/numbers, check speed of ALL extra plugins (Google it), check you host's speed.
Irrelevant. I've seen plenty of people using them and STILL have slow sites. It's how the site itself is setup that's the main problem.
e.g. I used to use Hostgator Business Cloud and had great loading speeds for my sites and another user here using them as well had terrible loading speeds. The hosting was not the problem. The problem was how his site was setup.
Bottom line, if the currency switcher alone could slow a site by 7 seconds, EVERYONE who uses it would have the same complaint. But I've never heard anyone complaining about it and I don't experience it on 8 separate sites that use it.